Muireann DeClár (10) from Navan, Co Meath, who is severely allergic to eggs, was sitting on the side of an advertising truck bearing a 'No' campaign ad when at least one youth started throwing missiles, including eggs.

The youngster suffered a severe allergic reaction, which caused a rash which spread across her face, neck and shoulder. Her mother Aoife said her daughter's face had swollen so much that her eye closed up.

"We were standing at the Navan Shopping Centre and there were kids running around. We had stopped for photographs at the 'No' billboard and there was a row of children sitting next to it," said Ms DeClár.

"The children ranged in age from three to 10. There were also three babies in buggies. I suddenly heard Muireann screaming: 'I'm allergic to egg'. I turned around and it was dripping down her face.

"She was hysterical. She has severe allergies to egg and has gone into anaphylactic shock in the past.

"I brought her home as quick as I could because she had developed breathing difficulties. I immediately treated her with an Anapen adrenaline injector. She didn't consume any of the egg, but she's so sensitive to it that it only has to touch her skin for her to have a reaction."

Gardaí are investigating the incident and urged witnesses to come forward with information.

The event, staged by campaign group Mothers and Fathers Matter, was being led by Paddy Manning.

"While the attackers had no way of knowing that the child had an allergy, they had every way of knowing that she was a child of about 10 years old," said Mr Manning.

Vote

Meanwhile, Mothers and Fathers Matter has claimed politicians from all of the main political parties privately intend to vote 'No'.

The campaign said its representatives had spoken to TDs and senators who were in favour of a 'No' vote despite the stance of their parties. But group spokesman Keith Mills declined to name individual TDs and senators whom he said were against extending marriage for same-sex couples.

He said the representatives belonged to all of the main political parties. Mr Mills said thousands of people were "silenced" because they felt they would be targeted if they spoke in opposition to same-sex marriage.